The invention relates to an inflatable gas bag for an occupant restraint system in a vehicle and a method for manufacturing such a gas bag.
Occupant restraint systems with gas bags, frequently also referred to as airbags, which are automatically inflated in the case of a serious accident are nowadays installed in a plurality of passenger cars both on the driver's side and on the passenger's side in order to possibly avoid, in the case of a serious frontal impact of the vehicle, potential head and chest injuries of the vehicle occupants which are seated in the front. Such systems which essentially consist of a mostly pyrotechnical gas generator and a gas bag as well as of the associated control electronics are increasingly employed in the lateral area of passenger cars in order to dampen and distribute the forces acting upon the vehicle in the case of a side impact over a larger area and thus decrease the injury hazard for the vehicle occupant who is seated on the impact side. Such laterally arranged impact protection systems with gas bag, which are also referred to as sidebags, are, for example, accommodated in the vehicle doors or in the backrests.
On the basis of the predominantly positive experience gained with such impact protection systems which comprise a gas bag the trend exists to employ such systems on a wider scale in trucks and buses as well.
Depending on the task which an occupant restraint system of the initially mentioned type is to fulfill, the gas bag in its inflated state must have a precisely defined shape in order to achieve the optimum effect. The so-called driver airbags in their inflated state are, for example, approximately balloon-shaped, while the so-called passenger airbags in their inflated state are approximately cushion-shaped. Side airbags, in turn, frequently still have intricate shapes in order to be able to comply with the requirements imposed on them.
In addition, gas bags must fulfill two contradictory requirements: On the one hand they must be inflatable as rapidly as possible when required; on the other hand they have to provide as large a distance as possible between the vehicle occupant to be protected and the object with which the vehicle occupant must not collide. While the first requirement calls for a small gas bag volume, a relatively large gas bag volume is the result of the second requirement. The existence of impact protection systems with a gas bag, however, is only justified if their protective effect is as good as possible so that nowadays large gas bag volumes are preferred in order to achieve an optimum protective effect.
Conventional gas bags consist of two or more individual textile parts which are cut from textile flat material and subsequently sewn together. Accordingly, two circularly made-up two-dimensional textile parts are generally sewn together for a driver's airbag. Upon inflating these conventionally manufactured gas bags into their three-dimensional state which they must assume in order to achieve the desired protective effect, creases occur in particular in the seam area, which extend perpendicular to the seams. These creases result in high stress peaks in the seam area which is already weakened by the seam. In order to avoid bursting of the gas bag in the seam area under load, very heavy fabrics are used in the manufacturer of the gas bag. These heavy fabrics in conjunction with the relatively large gas bag volume selected for achieving a good protective effect result in conventional gas bags being relatively heavy. In order to nevertheless ensure the rapid inflation when necessary, larger gas generators have to be employed which are capable of correspondingly rapidly accelerating the relatively large mass of the gas bag. Large pyrotechnical gas generators in turn are disadvantageous in that during inflation the temperature of the gas developed by the gas generator reaches very high values and that these high temperatures can affect the gas bag and destroy its fabric. In addition, a gas bag with a larger mass unfolds only later due to its higher inertia so that the hot gases developed by the gas generator act longer on the still folded fabric which is located near the gas generator. In order to not destroy the gas bag fabric as a result of this bombardment with the combustion gases great yarn thicknesses (approx. 250 to 700 dtex) are employed which ensure that the fabric does not fail even then when glowing particles impinge on the fabric and individual threads start melting.